Help sought: Panel temp sensor dead in 13-year old flat panel water heater system.

[windbag]

Hi folks

I have a system semi-professionally installed in July 1999 (13 years ago), which has been running fine until now.
Today, our first proper sunshine day here in the UK since last summer, I found steam issuing from the pressure relief valve.

Looking at the temperature sensor display unit, the problem is the temperature sensor in the panel, which is registering -14C (!)
The lower tank temperature is registering fine.
I'm competent electrically, so I delved into the control box, which is a Suntech "Sunhound 1" unit. It has mains power OK.
The panel sensor is connected via UK phone wire using two cores doubled up for each of the three connections made.
These mirror the two hot water tank sensors in having three connections, each with a green, red & blue colour-coded wires.

What type of sensor are these likely to be?
Can I start diagnosing the fault from the control box end - i.e. tell the difference between a dead sensor or a disconnected cable, for example?

If folk know of a troubleshooting guide to point me at, great, or detailed advice on how to check would also be welcome.

Thanks

PS I manually cooled down the panel by connecting the system pump directly to the mains rather than via the control box relay.
It is basically working OK, just not getting the right logic signal to the mains relay in the control box when the panel is hotter than the tank water.
PPS I say "semi-professionally installed" as it was by a start-up company that no longer exists. They provided scant details of the units I actually received.
The Suntech company who have their name on the "Sunhound 1" unit are nothing to do with the American, Indian or Hong Kong/Chinese companies who currently use the name.
Googling Suntech "Sunhound 1" yields nothing useful!

[Mike90250]

Bummer. Looks like time to buy a new differential controller.

[MikeSolar]

Most likely it is a PT1000 thermister. I has been the standard through europe for years. Look up Resol UK for a dealer near you.

To be sure, take off one of the good thermisters and measure it at around 25C, then at a colder or hotter temp to see if it goes up or down. That will give you more info.

[LucMan]

Disconnect power! Then
Switch the lower tank thermister wires to the panel connections in the controller. Reconnect power. The temp readout for the panel now should be the same as the lower tank read before you disconnected the wires if the controller is good.

[windbag]

Bummer. Looks like time to buy a new differential controller.

The controller is working AFAIK, it's the SENSOR that has gone down.

[windbag]

Most likely it is a PT1000 thermister. I has been the standard through europe for years. Look up Resol UK for a dealer near you.

To be sure, take off one of the good thermisters and measure it at around 25C, then at a colder or hotter temp to see if it goes up or down. That will give you more info.

It thought thermistors had two terminals - so why does it/the others have three terminals?

I did try a basic resistance measurement in situ with no power, and got nothing but an open circuit reading for any combination of probes on the three terminals on any of the three sensors.

I will be trying again when I know which sensor is which & properly disconnected from the controller in an hour or two; will report back.

[windbag]

Look up Resol UK for a dealer near you.

There is only one Resol UK dealer (Secon) - their website shows loads of sensors (including PT1000), but all are two-cable units with read and white coded cables, not three-cable green/red/blue connections.

[Mike90250]

The controller is working AFAIK, it's the SENSOR that has gone down.

Right, just like with a car, when the ash tray fills up, you find you can't buy a new, empty one, and you have to buy a new car

I love all the non-documented stuff, 3 wire, 2 wire, parts not made anymore - buy a new $500 box because a $4 sensor is not made anymore.

[windbag]

More detailed info

Got into the control box with a torch this time, and can see the connector labels.

All the sensors have a zero and +5V supply (blue & red respectively), with the sensing voltage returning on the green wire.
The +5V supply is fine, reading 5.1V on my DVM.

The working tank sensor is mounted/sealed into a 6mm (

[MikeSolar]

[QUOTE=windbag;46510]Got into the control box with a torch this time, and can see the connector labels.

All the sensors have a zero and +5V supply (blue & red respectively), with the sensing voltage returning on the green wire.
The +5V supply is fine, reading 5.1V on my DVM.

The working tank sensor is mounted/sealed into a 6mm (

[windbag]

Not a thermocouple - but might be a Zener with temp-variable breakdown voltage

... think you need a new control. Sorry

Gosh, folk here are really quick to throw up their hands and "buy a new one". Not my approach!

Right so you have a control that uses thermocouples.

I don't understand. All the thermocouples I have ever used (including the one I have to hand for a multimeter) have two wires and require no power - but do need very careful connection methodologies, which is why I'd have thought they wouldn't be used in a domestic fitted unit.

Testing the thermocouple I have, it measures ~ 15 Ω whichever way I connect across it - so the behaviour doesn't correspond in any way to working sensor I have.

It DOES correspond with a thermistor/resister in series with a centre-tap, but I can't see why you'd put power and the balancing resistor in the sensor like this, so I think it is unlikely that it really is that either.

I'm hoping someone on this forum is familiar with the precision temperature sensors such as the LM135 which is available as a three-wire TO92 package which could easily be mounted in the head I've described, and which I've certainly seen cited as used in domestic solar installations. Thomson and National Semiconductor (& probably many others) make these, for example.

From the Thomson data sheet:

"The LM135, LM235, LM335 are precision temperature sensors which can be easily calibrated. They operate as a 2-terminal Zener and the breakdown voltage is directly proportional to the absolute temperature at 10mV/

[MikeSolar]

[QUOTE=windbag;46553]Gosh, folk here are really quick to throw up their hands and "buy a new one". Not my approach!



I don't understand. All the thermocouples I have ever used (including the one I have to hand for a multimeter) have two wires and require no power - but do need very careful connection methodologies, which is why I'd have thought they wouldn't be used in a domestic fitted unit.

Testing the thermocouple I have, it measures ~ 15 Ω whichever way I connect across it - so the behaviour doesn't correspond in any way to working sensor I have.

It DOES correspond with a thermistor/resister in series with a centre-tap, but I can't see why you'd put power and the balancing resistor in the sensor like this, so I think it is unlikely that it really is that either.

I'm hoping someone on this forum is familiar with the precision temperature sensors such as the LM135 which is available as a three-wire TO92 package which could easily be mounted in the head I've described, and which I've certainly seen cited as used in domestic solar installations. Thomson and National Semiconductor (& probably many others) make these, for example.

From the Thomson data sheet:

"The LM135, LM235, LM335 are precision temperature sensors which can be easily calibrated. They operate as a 2-terminal Zener and the breakdown voltage is directly proportional to the absolute temperature at 10mV/

[russ]

Calibrating a TC is nothing more than comparing it to a known temperature.

There is nothing to calibrate - only two wires and a cold junction.

[MikeSolar]

Calibrating a TC is nothing more than comparing it to a known temperature.

There is nothing to calibrate - only two wires and a cold junction.

True, and some devices allows you to alter the program to accept different curves for the thermisters or TCs but not typically simple solar controllers. We use a lot of DDC controls and dataloggers where we have to calibrate device to the curve of the sensor for proper operation.

The bottom line here is that unless the OP can find the same sensor (assuming there are some markings on it) and there is nothing wrong in the control (such as damage from lightning), he is better off picking up a RESOL or similar control.

[windbag]

True, and some devices allows you to alter the program to accept different curves for the thermisters or TCs but not typically simple solar controllers. We use a lot of DDC controls and dataloggers where we have to calibrate device to the curve of the sensor for proper operation.

The bottom line here is that unless the OP can find the same sensor (assuming there are some markings on it) and there is nothing wrong in the control (such as damage from lightning), he is better off picking up a RESOL or similar control.

I 98% sure the controller is AOK. I "just" need replacement sensors.

I almost wish they WERE a thermocouples. There are only a few types, and monitoring microvolts Vs temp would tell me which.
On the other hand, I'm glad they aren't as thermocouples can have a real problem with long connections, and you need proper compensating cables to ensure temperaure variations at connections along the path don't mess up the results. Plus the issue of very small signals being susceptible to RF etc. I used to work with thermocouples in large scale field trials, so I have experience here.

But as I said, they are NOT thermocouples, AFAI can tell electrically.

I have the dead sensor in my hands - you guessed it, no markings - so I'm going to have to try and get the transducer out of the tube.

Wish me luck!